And now the force, in its most general term / is q1q2 over 4 pi epsilon zero, which is the conversion factor r squared.

库仑力的最基本形式,就是，其中r是一个变量。

麻省理工公开课 - 固态化学导论课程节选

The basic definition-- the expected value of some random variable x--E--I guess I should have said that a random variable is a quantity that takes on value.

最基本的定义,某一个随机变量X的期望值E,我应该提到过,随机变量是一个可以取值的数

耶鲁公开课 - 金融市场课程节选